Cochlear implants (CIs) and other inner ear prostheses are one option to help profoundly deaf or severely hearing impaired persons. Unlike conventional hearing aids that just apply an amplified and modified sound signal; a cochlear implant is based on direct electrical stimulation of the acoustic nerve. Typically, a cochlear implant stimulates neural structures in the inner ear electrically in such a way that hearing impressions most similar to normal hearing is obtained.
A normal ear transmits sounds as shown in FIG. 1 through the outer ear 101 to the tympanic membrane (eardrum) 102, which moves the bones of the middle ear 103 (malleus, incus, and stapes) that vibrate the oval window of the cochlea 104. The cochlea 104 is a long narrow duct wound spirally about its axis for approximately two and a half turns. It includes an upper channel known as the scala vestibuli and a lower channel known as the scala tympani, which are connected by the cochlear duct. The cochlea 104 forms an upright spiraling cone with a center called the modiolus where the spiral ganglion cells of the acoustic nerve 113 reside. In response to received sounds transmitted by the middle ear 103, the fluid-filled cochlea 104 functions as a transducer to generate electric pulses which are transmitted to the cochlear nerve 113, and ultimately to the brain.
Some persons have partial or full loss of normal sensorineural hearing. Cochlear implant systems have been developed to overcome this by directly stimulating the user's cochlea 104. A typical cochlear prosthesis may include two parts: the audio processor 111 and the implanted stimulator 108. The audio processor 111 typically includes a microphone, a power supply (batteries) for the overall system and a processor that is used to perform signal processing of the acoustic signal to extract the stimulation parameters. The audio processor 111 may be an external behind-the-ear (BTE-) device, may be a single unit that integrates the processor, battery pack and coil (e.g., the RONDO Single Unit processor from MED-EL Elektromedizinische Geraete GmbH) or may be implantable.
The stimulator 108 generates the stimulation patterns (based on the extracted audio information) that is sent through an electrode lead 109 to an implanted electrode array 110. Typically, this electrode array 110 includes multiple electrodes on its surface that provide selective stimulation of the cochlea 104. For example, each electrode of the cochlear implant is often stimulated with signals within an assigned frequency band based on the organization of the inner ear. The assigned frequency band of an electrode is typically based on its placement within the cochlea, with electrodes closer to the base of the cochlea generally corresponding to higher frequency bands.
The connection between a BTE audio processor and stimulator is usually established by means of a radio frequency (RF-) link. Note that via the RF-link both stimulation energy and stimulation information are conveyed. Typically, digital data transfer protocols employing bit rates of some hundreds of kBit/s are used.
For optimal hearing performance, repeated adjustment of strategy-related map parameters, that are used for programming a cochlear implant prosthesis system to the specifications and needs of its user may be performed from time to time. This is especially true for the electric dynamic range (DR), which is defined by the maximum comfortable loudness (MCL) and threshold (THR)-charge level for each electrode, and which influences performance strongly. The MCL indicates the level at which perceived sound is loud but comfortable; while the THR typically indicates the threshold of hearing. Typically, an increase in MCL or M-level stimulation amplitudes has been found during the first year post implantation, while at the same time electrode impedance values (EIVs) decrease. Usually, stabilization of stimulation levels and EIVs occurs after approximately three months.
In clinical routine, the map parameters are usually adjusted in several sessions by an audiologist on a fixed schedule. Additional visits may be necessary if a CI patient complains about dysfunction or non-optimal functionality of the CI system.
Commonly, progressive maps are used for the run-in period, i.e., during the first few months, several maps with progressively increasing MCL amplitudes (by a certain percentage) are generated. The CI patient is instructed by the clinician to manually switch between these maps. With progressive maps, the anticipated charge increase that may occur during this time period may be managed without additional clinical visits. Unfortunately, progressive maps comprise the risk of over-stimulation, for example, if created maps can not be activated at the time of map creation due to the involved charge values exceeding the actual dynamic range of the patient.
Since both the course of map stabilization and the optimal re-fitting intervals vary individually from patient to patient, no optimal universal time schedule can be defined. Generally, short visit intervals to the clinic may improve listening performance in some patients, but will also lead to higher workload for clinics. Furthermore, more frequent visits to the clinics may be unreasonable due to the often considerable travelling, time and cost burdens placed on the patient.